1. Field of the Invention
The invention pertains to thin-film platinum resistor devices which are useful in measuring temperature over a wide range.
2. Description of the Prior Art
Platinum in wire or ribbon form has long been considered a primary resistance and temperature measuring standard because of its chemical inertness and physical stabiliy. For use as a resistance thermometer, where a measurement is used to determine temperature, platinum has the further advantage of possessing a high temperature coefficient of resistance which increases the sensitivity of the thermometer to temperature change.
However, the use of platinum in wire form has been found to possess a number of practical limitations. In many applications it has been found difficult to achieve a good thermal bond between the platinum and the object of which the temperature is being measured. A wire or layer of platinum of sufficiently thin cross section to produce an absolute resistance sufficiently high for many applications has resulted in a very fragile device.
Platinum deposited upon a semiconductor, ceramic, or other substrate and separated therefrom by a thermally electrically insulating layer has been desired as a device to overcome many of the problems of the prior devices. Unfortunately, platinum exhibits a poor adherence to most practical substrate and thermally insulating layer materials.
Platinum has been used as a conductive layer in several different integrated circuit configurations. In each of these, however, the layer of platinum was joined to the underlying substrate through a thin adhesion layer of chromium or titanium. However, a device thusly fabricated will not suffice for temperature measuring applications as the chromium or titanium layer changes the resistance of the platinum layer and neither one of these materials possesses the same chemical inertness and physical stability characteristics as platinum. If a device using a chrome or titanium adhesion layer were annealed as would be done in the normal fabrication of such a device, molecules of chromium or titanium would diffuse into the platinum layer changing its electrical properties and making the film unstable for use over a wide range of temperatures.